In EP 1 074 296 (U.S. Pat. No. 6,427,985) a stacked packing is described where the individual packings are each formed of two separate packing layers of different geometry. Here the lower packing part is of tighter geometry than the upper packing part. The packing is operated such that the lower packing part is made to bubble with high mass transfer. The overlying coarser packing layer separates out the bubbles and has film flow so that it works like a conventional packing.
When such a packing is used, it is very sensitive when not set perfectly horizontally, especially when the column diameter is greater than 1 m. When tipped there is uneven liquid distribution across the column. Thus there are liquid-filled zones with lower gas throughput. This nonuniformity has a bad effect on the otherwise high separation capacity.